In perpendicular magnetic recording, the magnetizations in the adjacent bits do not face each other, and therefore a stable recorded state can be achieved which is essentially suitable for high recording density. A perpendicular magnetic recording medium has a structure where a soft magnetic underlayer, an intermediate layer, and a magnetic recording layer are mainly stacked. The soft magnetic underlayer suppresses expansion of a magnetic field generated from a magnetic head so as to efficiently magnetize the magnetic recording layer. The intermediate layer magnetically separates the soft magnetic underlayer and the magnetic recording layer, and controls crystalline orientation of the magnetic recording layer. For the magnetic recording layer, a granular-type recording layer including a CoCrPt ferromagnetic alloy added with an oxide such as SiO2 is typically used, which is regarded to be low in medium noise, and strong in thermal demagnetization compared with a previous CoCrPt medium.
One way to further improve performance or increase recording density is to reduce medium noise in the magnetic recording layer. In addition, a distance between the soft magnetic underlayer and the magnetic head may be reduced. As described before, the soft magnetic underlayer prevents expansion of a magnetic flux generated from the recording head, and thus assists writing of information into the magnetic recording layer. Therefore, the distance between them is reduced, thereby a magnetic field gradient of the recording head is steepened, and consequently information can be more efficiently recorded. As a method of reducing the distance between the soft magnetic underlayer and the magnetic head, reducing flying height of the magnetic head, reducing thickness of a protective film or a lubricant film, and furthermore reducing thickness of the magnetic recording layer or an intermediate layer are possible. Reduction in thickness of the protective film or the lubricating film is limited from the viewpoint of reliability. In addition, reduction in thickness of the magnetic recording layer problematically leads to degradation in thermal stability of recorded magnetization, increase in noise, and degradation in signal quality. Since the intermediate layer has an important role for controlling crystalline orientation of the magnetic recording layer, it has been an important problem that thickness of the intermediate layer is reduced while keeping properties of the magnetic recording layer intact.
A medium configuration, which has been proposed in the past, has a large thickness of an intermediate layer, and when the intermediate layer is simply thinned, properties of the recording layer are degraded, and therefore a magnetic recording medium having excellent recording/reproducing characteristics has been difficult to achieve.
Therefore, a magnetic recording medium which retains excellent recording/reproducing characteristics while reducing the thickness of the intermediate layer is desired in the art.